Preparation of fatty acid ester mixtures enriched in unsaturates

ABSTRACT

A PROCESS FOR PREPARING FATTY ESTER MIXUTRES ENRICHED IN UNSATURATES FROM NATURAL FATS AND OILS COMPRISING TRANSESTERIFYING SAID FATS AND OILS WITH A LOWER ALCOHOL AND SELECTIVELY EXTRACTING THE UNSATURATED FATTY ACID ESTERS WITH A TWO-HASE SOLVENT SYSTEM COMPRISING A HYDROCARBON AND GAMMA-BUTYROLACTONE ($-BUTYROLACTONE). THE ESTERS ARE USEFUL IN FOODS AND PAINTS.

United States Patent 3,755,385 PREPARATION OF FATTY ACID ESTER MIXTURES ENRICHED IN UNSATURATES James P. Hutchins, Springfield Township, Hamilton County, Ohio, assignor to The Procter & Gamble Company, Cincinnati, Ohio No Drawing. Filed Mar. 24, 1971, Ser. No. 127,753 Int. Cl. C07c 67/06 US. Cl. 260410.9 R 10 Claims ABSTRACT OF THE DISCLOSURE A process for preparing fatty ester mixtures enriched in unsaturates from natural fats and oils comprising transesterifying said fats and oils with a lower alcohol and selectively extracting the unsaturated fatty acid esters with a two-phase solvent system comprising a hydrocarbon and gamma-butyrolactone ('y-butyrolactone). The esters are useful in foods and paints.

BACKGROUND OF THE INVENTION The present invention relates to a process for preparing and separating lower alkyl fatty acid esters on the basis of their degree of unsaturation.

Natural fats and oils, e.g., soybean oil, safflower oil, corn oil, palm oil, tung oil, lard oil, tallow oil and the like, consist of mono-, di-, and tri-glycerides of fatty acids containing from about 10 to about 22 carbon atoms. Certain of these fatty acids are unsaturated, that is, they contain one or more carbon-to-carbon olefinic double bonds, the more double bonds, the higher the degree of unsaturation. The presence of said double bonds causes the more highly unsaturated fatty acids to have unique and desirable properties over their more saturated counterparts. For example, the melting points of the unsaturated fatty acids and their esters are lower than those of the corresponding saturated acids and such unsaturated fatty acids find utility in the preparation of liquid shortenings, usually in the form of glyceride esters enriched in unsaturates. Likewise, the unsaturated fatty acids are used in drying oils in the paint industry, said drying properties being related to the cross-linking of olefinic bonds by air and hence, to the degree of unsaturation of the oils. It may therefore be seen that the utility of unsaturated fatty acids and their esters is Well recognized in the art and a method for separating the more highly unsaturated materials from their more saturated counterparts present in natural fats and oils is of commerical interest.

Since the esters or fatty acids having various degrees of unsaturation are similar in molecular structure and physical properties, their separation has long been recognized as being difiicult and ordinary distillative procedures are not commercially suited for this purpose. At the same time, these unsaturated materials are detrimentally discolored by excessive heat and polymerization sometimes occurs at high temperatures by reaction with oxygen; hence, separation is best achieved by extraction procedures, usually carried out at temperatures near room temperature. For most commercial purposes it is not necessary to achieve complete separation of the saturated and unsaturated fatty materials and it is only necessary to separate them into an extract fraction which is enriched in the desired unsaturated material and a corresponding rafi'inate fraction which is depleted in unsaturated material. The

fraction enriched in unsaturates is suitable for use in the preparation of glycerides and other acids and esters needed to impart desirable properties to drying oils, liquid shortenings, etc., as noted above, or is useful per se in such compositions.

It is an object of this invention to provide a method for securing mixtures of fatty acid esters enriched in unsaturates from natural fats and oils of the type hereinabove detailed. (The fatty acid esters having one or more olefinic double bonds prepared herein are of various types and are referred to collectively as unsaturates.) It is another object of this invention to provide a twophase solvent system comprising a hydrocarbon phase and a -butyrolactone phase capable of separating lower alkyl esters of fatty acids into a v-butyrolactone extract phase enriched in unsaturates and a hydrocarbon raffinate phase depleted in unsaturates. These and other objects are obtained by this invention as will become apparent from the following disclosure.

The concurrently filed application of Hutchins entitled Preparation of Fatty Acid Ester Mixtures Enriched in Unsaturates filed Mar. 24, 1971, Ser. No. 127,754, now abandoned, discloses another solvent system suitable for separating unsaturated fatty esters from saturated fatty esters.

DESCRIPTION OF THE INVENTION The instant invention encompasses a process for securing mixtures of the lower alkyl esters of fatty acids eu riched in unsaturates from fats or oils comprising: (1) trans-esterifying a fat or oil containing unsaturated fatty esters or unsaturated fatty glyceride esters with a lower alcohol at a temperature from about 50 F. to about 350 F. in the presence of a mineral acid or base catalyst, preferably an alkali metal derivative of a lower alcohol of the type herein described, to prepare the lower alkyl ester derivatives of the fatty acids present in said fat or oil; (2) contacting the mixture of lower alkyl esters of the saturated and unsaturated fatty acids prepared in step (1) with a two-phase solvent system comprising a liquid hydrocarbon and 'y-butyrolactone at a temperature from about 0 F. to about F.; and (3) separating the resultant extract phase and rattinate phase and recovering the lower alkyl esters of fatty acids from the extract phase.

The fats and oils disclosed hereinabove as suitable sources for unsaturated fatty acids all contain said fatty acids primarily in the form of glyceride esters. In step (1) of this invention these fatty glyceride esters are converted into the corresponding alkyl esters so that the unsaturates can be more readily removed from the saturated materials. From the foregoing discussion it will be recognized that unsaturated acids and esters having different degrees of unsaturation have very similar properties to one another and to the corresponding saturated acids and esters, respectively, and that extractive separation of these various materials depends on very minor solubility differences. For example, the free acid forms of both the saturated and unsaturated materials are relatively soluble in the polar solvent used herein and separation of these materials is not satisfactory when the extraction is carried out with the polar acid form of the fatty materials. For this reason, the fats and oils are converted into the alkyl ester form of the saturated and unsaturated fatty acids, which is not as polar as the acid form, so that minor solubility differences can be exploited to achieve separation. At the same time, however, it is necessary that the ester form of the fatty materials be chosen so that the non-polar characteristics of the two classes of materials are not unduly accentuated. For example, both the saturated and unsaturated fatty acids esterified with long chain alcohols tend to remain in the non-polar raffinate fraction after extraction since such materials do not have sufiicient polar solvent solubility to be extracted. For this reason, it is necessary when using the extraction system described herein to convert the acids to their lower alkyl esters, i.e., the methyl, ethyl and propyl esters. Such lower alkyl esters are neither excessively polar so as to be unduly soluble in the polar extract solvent herein, nor are they so highly non-polar as to remain exclusively in the non-polar rafiinate solvent.

In step (1) of this process the lower alkyl esters of the unsaturated and saturated fatty acids are prepared from the natural fats and oils of the type hereinbefore noted by heating said fat or oil with a lower alcohol in the presence of a mineral acid (e.g., H 80 HCl, H PO or base catalystat a temperature from about 50 F. to about 350 F. for about minutes to 24 hours and recovering the lower alkyl esters from the glycerol which is formed by physical separation, all in the well-known to those skilled in the art. Preferred catalysts herein include the alkali metal salts of lower alcohols. In this trans-esterification it is preferred to employ at least about three eqivalents of the lower alcohol per equivalent of glyceride ester to provide sufiicient reactant to completely convert the acids in any triglycerides in the fat or oil to the lower alkyl ester form. Less alcohol can be used if product yield is not of concern; a two-fold to three-fold excess of alcohol can be used to provide both reactant and reaction solvent. The catalyst, e.g., the alkali metal a1- coholate, is used in amounts ranging from about 0.1 equivalent per equivalent of alcohol. Large excesses of the catalyst represent an economic waste and are to be avoided for this reason. Use of from about 0.01 to 1.0 equivalents of the mineral acid or base, e.g., alcoholate catalyst, for each equivalent of acid present in the fat or oil is satisfactory.

The alkali metal alcoholate catalysts preferred herein can be prepared by reacting the appropriate alkali metal, usually sodium or potassium for economic reasons, with the lower alcohol, i.e., methanol, ethanol or propanol. Alternatively, a solution of alkali metal hydroxide, e.g., sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like, in the lower alcohol serves the same purpose herein as the metal alcoholate and provides lower alkyl esters of saturated and unsaturated fatty acids by heating with the glycerides present in the fats and oils in the aforementioned manner. Alkali metal alcoholates especially suited for use herein include sodium methoxide, sodium ethoxide and sodium propoxide, with sodium methoxide being preferred. Methanol, ethanol and propanol, and mixtures thereof, are the preferred lower alcohols. A solution of sodium hydroxide in methyl alcohol, ethyl alcohol or propyl alcohol is likewise preferred herein for converting the fatty gycerides to a mixture of glycerol and lower alkyl fatty acid esters suitable for use in the extraction procedure of step (2). A solution of sodium methoxide in methanol is especially preferred for use in the transesterification step (1), herein.

The extraction step (2) of this process employs a twophase solvent system com-prising a hydrocarbon, as described below and -butyrolactone, which is commercially available. Up to about by weight, of water can be present in the -butyrolactone to enhance the selective solvent properties thereof. However, since water reduces ester solubility, thereby decreasing the extraction rate, about 5% water (based on weight of 'y-butyrolactone) is preferred herein both to increase selectivity and to maintain extraction capacity.

The hydrocarbon used herein to enhance the selectivity of the process comprises any of the hydrocarbons which are liquid at the extraction temperatures in the range noted, and mixtures thereof. Hydrocarbons suitable for use herein include saturated linear and cyclic hydrocarbons having from about 5 to about 20 carbon atoms, unsaturated liquid cyclic and linear hydrocarbons in the same range, and the liquid aromatic hydrocarbons, e.g., benzene and toluene. Branched chain and straight chain hydrocarbons are equally suitable for use herein; saturated hydrocarbons are preferred. Exemplary hydrocarbons which can be used herein include pentane, cyclopentane, hexane, cyclohexene, octane, 3-methyloctane, decene, undecane, dodecane, benzene, eicosane, cycloeicosane, 4,5-diethyldecane and the like, and mixtures thereof. Hydrocarbon mixtures such as mineral oils, liquid parafiins, distilled kerosene fractions and the like, are also suitable to secure the raffinate phase in the extraction step of the present process. Hexane is especially preferred for use herein.

In the extraction procedure of step (2) the mixture of lower alkyl esters of saturated and unsaturated fatty acids prepared in step (1) is contacted with the two-phase solvent system and the phases allowed to separate. contact between the two-phase solvent system and the mixture of fatty acid esters can be achieved by batch mixing or by use of any of the commercially available extraction apparatus involving countercurrent, cocurrent continuous, crosscurrent continuous, etc., extraction techniques. Contact time between the two-phase solvent system and the ester mixture is usually in the range from about 0.5 minutes to about 60 minutes, more preferably from about 2 minutes to about 4 minutes. The extraction is carried out at temperatures from about 0 F. to about 110 F., more preferably from about 40 F. to about F. At temperatures higher than about F., the selectivity of the 'y-butyrolactone phase for the unsaturated esters is reduced.

The amount of the two-phase solvent system used here in is not critical to achieve selective extraction but is commonly based on the total weight of the esters being extracted. To maintain optimum selectivity, the Weight of esters dissolved in the 'y-butyrolactone preferably should not be greater than 10% by Weight, of said 'y-butyrolactone. Most generally, from about 5 to 40 parts of the -butyrolactone is used per part of ester; a ratio of 20 parts 'y-butyrolactone to one part ester is preferred. About 0.5 to 3 parts of hydrocarbon phase is used for each part of ester.

Step (3) of the process involves separating the 'ybutyrolactone extract phase from the hydrocarbon raffinate phase and recovering the ester mixture enriched in unsaturates. More highly saturated esters can be recovered from the hydrocarbon solvent, if so desired. Alternatively, the hydrocarbon phase can be re-extracted with 'y-butyrolactone to secure additional unsaturated esters. Physical separation of the two phases is achieved by simply drawing-oif one phase from the other. Recovery of the desired unsaturated esters is accomplished by physical methods, e.g., by evaporation of the extract solvent.

The exemplary fats and oils hereinabove described as suitable sources for unsaturated fatty esters contain a variety of fatty acids such as oleic acid, linolenic acid, eleostearic acid, linoleic acid, ricinoleic acid, palmitoleic acid, petroselenic acid, vaccenic acid and the lke, primarily in the form of glyceride esters. Common saturated fatty acid glycerides present in such fats and oils include those of lauric acid, myristic acid, palmitic acid, stearic acid, and the like. By the process of this invention, the fatty materials containing these various acids are converted to mixtures of the lower alkyl esters of said acids and said esters are separated into a fraction enriched in unsaturates and one depleted in unsaturates. That is to say, there will be more olefinic double bonds in the esters in the extract phase than in the rafiinate phase. Certain fats and oils contain different unsaturated and saturated fatty acids, and different proportions thereof, than do other fats and oils. For example, soybean oil contains major amounts of oleic and linoleic acids, while whale oil contains major amounts of palmitoleic and palmitic acids. It is immaterial in the practice of this invention which unsaturated and saturated acids are present in the mixture of lower alkyl esters being prepared and separated. For example, the lower alkyl esters of oleic acid are separated from the lower alkyl esters of stearic acid by the extraction system used herein; the lower alkyl esters of linoleic acid are separated from the lower alkyl esters of lauric acid while the lower alkyl esters of linoleic acid are separated from the lower alkyl esters of stearic acid. In addition, fatty acids having a multiplicity of double bonds can be separated from fatty acids having fewer double bonds. For example, by this process the lower alkyl esters of linoleic acid, which have two double bonds, can be separated from the lower alkyl esters of oleic acid, which have one double bond. Likewise, the lower alkyl esters of linolenic acid, which have three double bonds, can be separated from the lower alkyl esters of linoleic acid. It can therefore be seen that by this invention it is possible to prepare extract fractions which are enriched in unsaturates. It is to be further recognized that steps (2) and (3) herein can be repeated on the enriched material to achieve nearly complete separation of the individual fatty acid esters based on their degree of unsaturation, if so desired.

While the lower alkyl esters of any of the fats and oils herein disclosed are suitably extracted and separated into fractions enriched in various unsaturates by this invention, soybean oil lower alkyl fatty acid esters, especially methyl esters, are preferred herein. Likewise, while this process can be used in general to obtain ester fractions enriched in the lower alkyl esters of unsaturated fatty acids, it is particularly suited for separating the lower alkyl esters, especially the methyl esters, of oleic and linolenic acids and for separating the lower alkyl esters, especially the methyl esters, of linoleic and linolenic acids, thereby afiording, in each instance, an extract phase enriched in unsaturates.

From the foregoing it can be seen that this process separates all manner of mixtures of the lower alkyl esters above was contacted with an extraction medium comprising 1.0 g. of hexane and 10 g. of BLO at 75 C. In a third run, 1.0 g. of the fatty acid methyl ester mixture was contacted with an extraction mixture comprising 2 g. of hexane and 20 g. of BLO containing 5% by weight of water at 75 C. In a fourth run, 1.0 g. of the ester mixture was contacted with 1.0 g. of hexane and 10 g. of BLO containing 5% water. In still another run, 2.1 g. of the above ester was contacted with 21 g. of BLO at 0" F.

Step 3 Wt. fraction A in 'y-butyrolactone Wt. fraction B in 'y-butyrolactone 6- Wt. fraction A in hydrogen Wt. fraction B in hydrogen wherein A and B represent the lower alkyl ester of the fatty acids being separated. For example, [3 is the fl-factor for the separation of an ester having these double bonds from one having two; [3 is the factor for the separation of di-unsaturates from mono-un saturates. At B-factors of about 1.5, and less, the process becomes uneconomical because of the need for unwieldy extraction equipment. Since the i -factor remains above 1.5 when the total amount of ester in the extract phase is not greater than about 10%, by weight, of said extract phase, conditions are preferably adjusted to maintain this percentage.

TABLE 1 Ester composition, wt. percent Grams ester in- BLO phase Hexane phase Grams BLO Hexane Lino- Lino- Lino- Lino- Ester Hexane BLO phase phase Oleate leate lenate Oleate leate lenate 1 BLO with 5% water. 2 Experiment E run at 0 F. all others at 75 F. of fatty acids into an extract phase enriched in unsaturates. The following examples illustrate the present TABLE 2 process.

EXAMPLE Gram ester 1u BLO Hexane Temp., Step 1 Run phase phase F. 62 183 2- 0.0095 0.38 75 2.05 2.02 The methyl esters of soybean 011 were prepared as fol- 1 g8 lows: 1500 g. of soybean oil was heated at 250 F. to 95 300 F. for 30 minutes with nitrogen sparge under vacg; uum. After cooling the oil, 285 g. of methanol containing 34 30 10.2 g. of sodium methoxide (mixed under nitrogen) was 23 i i :3 added thereto. The total mixture was refluxed for one 90 1.0 g. of the ester mixture obtained in step (1) was contacted with an extraction medium comprising 20 g. of -butyrolactone (BLO) and 2 g. of hexane at 75 F. In a second run, 1.0 g. of the ester mixture obtained 1 BLO containing ca. 5% water, by weight. 2 No hexane used.

The data indicate that the selectivity of the extraction is increased: (a) by use of a hydrocarbon solvent in conjunction with the BIJO; (b) at lower temperatures within the range; and (c) by adding water to the BLO phase. A compromise between extraction selectivity and capacity can be achieved by varying these conditions.

In the above process the BLO is used at a 50:1, :1, 2:1 and 1:1 weight ratio to the esters being extracted, respectively, with equivalent results. The hexane is respectively used at ratios 50:1, 20:1 and 1:1, based on ester, with equivalent results.

In the above process, the soybean oil is replaced by an equivalent amount of palm oil, safilower oil, whale oil, corn oil, lard oil, tallow oil, tung oil and cottonseed oil, respectively, and equivalent results are secured in that the methyl esters of the fatty acids of these oils are separated into an extract phase enriched in unsaturates and a raifinate phase depleted in unsaturates.

In the above process, the methanol-sodium methoxide is replaced by an equivalent amount of ethanol-sodium ethoxide, propanol-potassium propoxide, a 1 molar solution of sodium hydroxide in meth'yl alcohol, and a 1 molar solution of sulfuric acid in ethyl alcohol, respectively, and equivalent results are secured in that the fatty glyceride esters are converted to their respective methyl-, ethyl-, and propyl-esters and are separated into an extract fraction enriched in unsaturates and a raifinate fraction depleted in unsaturates.

In the above process, the hexane is replaced by an equivalent amount of octane, nonane, hexadecane, cyclohexene, petroleum ether, kerosene, and light mineral oil, respectively, and the extraction is carried out at 0 F 50 F. and 110 F., respectively, and equivalent results are obtained.

What is claimed is:

1. A process for securing mixtures of the lower alkyl esters of fatty acids enriched in unsaturates from fats or oils comprising: (1) trans-esterifying a fat or oil containing unsaturated fatty esters or unsaturated fatty glyceride esters with a lower alcohol at a temperature from about 50 F. to about 350 F. in the presence of a mineral acid or base catalyst to prepare the lower alkyl ester derivatives of the fatty acids present in said fat or oil; (2) contacting the mixture of lower alkyl esters of the saturated and unsaturated fatty acids prepared in step ('1) with a two-phase solvent system comprising a liquid hydrocarbon and 'y-butyrolactone at a temperature from about 0 F. to about 110 F.; and (3) separating the resultant 'y-butyrolactone extract phase and rafiinate phase and recovering the lower alkyl esters of unsaturated fatty acids from the extract phase.

2. A process according to claim 1 wherein the fat or oil containing the unsaturated fatty esters or unsaturated fatty glyceride esters is selected from the group consisting of soybean oil, cottonseed oil, saffiower oil, corn oil, palm oil, tung oil, lard oil and tallow oil.

3. A process according to claim 1 wherein the lower alcohol used to prepare the lower alkyl esters of the fatty acids present in the fat or oil is selected from the group consisting of methanol, ethanol and propanol.

4. A process according to claim 1 wherein the catalyst is an alkali metal salt of a lower alcohol.

5. A process according to claim 1 wherein the catalyst is selected from the group consisting of sodium methoxide, sodium ethoxide and sodium propoxide.

6. A process according to claim 1 wherein the 'y-butyrolactone contains about 5% water, by weight.

7. A proces according to claim 1 wherein the total ester dissolved in the 'y-butyrolactone is not greater than 10%, by weight, of said 'y-butyrolactone.

8. A process according to claim 1 wherein the liquid hydrocarbon is selected from the group consisting of hexane, light mineral oil, petroleum ether and kerosene.

9. A process according to claim 1 wherein the extraction step (2) is carried out at a temperature from about 40 F. to about F.

10. A process according to claim 1 wherein the oil is soybean oil, the lower alcohol is methyl alcohol, the catalyst is sodium methoxide, the two-phase solvent system comprises hexane and 'y-butyrolactone and the extraction temperature is about 7 5 F.

References Cited UNITED STATES PATENTS 7/l942 Goss et al. 260410.9 R X 8/1945 Glossop 260410.9

OTHER REFERENCES LEWIS GOTTS, Primary Examiner D. G. RIVERS, Assistant Examiner US. 01. X.R. 260-4285 

